In order to obtain a copper clad laminate with low dielectric properties, conventionally a benzoxazine resin and a styrene maleic anhydride were added into an epoxy resin to achieve a low dielectric loss, and an amine hardener is added thereto for improving peel strength, thereby using the technology approach to obtain a copper clad laminate with low dielectric properties.
The technology approach uses a low-cost epoxy resin. Epoxy resin is a resin with wide applicability, in which the ring-opening reaction of the epoxy group induces polymerization and crosslinking, and it has the advantages of absence of oxygen inhibition, high crosslinking, high conversion rate and high mechanical performance. However, epoxy resin inevitably causes volume shrinkage during the curing process and forms internal stress in the material which tends to cause warpage or crack and reduces the mechanical performance; the high volume shrinkage issue has become an urgent problem to be solved.
Recently, with the development of electronic technology, updating and new release of electronic products become faster, setting a higher challenge for the printed circuit industry and driving the development of future printed circuit technology toward multi-layer construction and high density interconnection. On the other hand, increase of layer number and trace density requires that a laminate as the base material of the circuit board to have lower thermal expansion, higher thermal resistance and smaller warpage, in the hope that it may, during the designing of the printed circuit, satisfy the impedance design and tolerate the thermal shock during the process.
In response to the demand of high density interconnection, the industry adopted high performance resin compositions including such as maleimide resin, benzoxazine resin and so on to fit this new technology approach. Maleimide resin is a high performance thermosetting resin having excellent thermal resistance, moist-heat resistance, dielectric properties and processability, and it is a common resin for modifying epoxy resin useful for making laminates. After ring opening, benzoxazine resin can form a structure similar to novolac resin, which effectively reduces water absorption rate of the cured system and increases chemical resistance, making it a popular resin for modifying epoxy resin for making laminates. However, the disadvantages are the unsatisfactory laminate properties, and there is still a need for lower thermal expansion, higher thermal resistance and smaller warpage; all these properties are specifically embodied in reflow shrinkage, storage modulus decrease rate, thermal resistance of high density holes, PCT thermal resistance after horizontal black oxide process and warpage height. Another drawback lies in the fact that the cost of maleimide is five folds of benzoxazine resin (Bz) and ten folds of epoxy resin; due to the limitations of process conditions, this situation is difficult to change.
Another approach is to use a third component, such as an allyl-modified bismaleimide, to improve the compatibility of epoxy resin and benzoxazine resin, so as to fit the needs of high density interconnect multilayer laminates. The disadvantage is that Tg and thermal resistance of the laminate is reduced.
Therefore, there is a need for developing a resin composition for high frequency applications and achieving the balance of thermal expansion, thermal resistance and low warpage in the system.